Previous attempts have been made to manufacture reliable interfaces for interconnection and separation systems between two adjoining components experiencing high loads and separation shocks. Such adjoining components may be found in, for example, fluid pipe systems, machines, or vehicles, including aerospace systems such as launch vehicles, launch vehicle payloads, and payload fairings.
A launch vehicle is used to launch a payload into orbit around the earth or toward a path outside of earth's orbit. The payload needs protection from the atmosphere at launch because the high temperatures and pressures created may damage a sensitive payload. A fairing (also referred to as a payload fairing or a launch vehicle adapter (“LVA”) fairing) is typically used to protect the payload or other portions of the upper stage before and during launch. A payload fairing surrounds the payload in the nose portion of the launch vehicle and a LVA fairing typically surrounds a portion of the spacecraft aft of the LVA or upper stage. The term “fairing” is used herein to reference all types of fairings. The fairing is detachably mounted to the upper stage of the launch vehicle. Once the rocket leaves earth's atmosphere, the fairing is separated from the launch vehicle and discarded to eliminate weight and prepare for separation of the payload.
Generally, in spacecraft launch vehicles, separation bolts secure at least the lower perimeter edge of a fairing to a separation ring, proximal to a horizontal separation plane, and may also interconnect edges of adjacent fairings, or the vertical separation plane(s). The separation bolts are spaced around the separation ring or on the edges of the fairings along the vertical separation plane(s) and include controlled charges. At the appropriate time, the charges are detonated to break the bolts and separate the fairings from the launch vehicle upper stage and/or from one another. However, shock waves and vibration are generated by these controlled charges as well as by the physical separation of the component pieces and disseminate through the body of the spacecraft. Shock waves and vibration (i.e., dynamic environments) can damage the payload.
Prior art fairing interconnection and separation systems use a variety of structures including a frangible joint at the base of the fairing ring, separation bolts and hinges, or a tongue and groove joint to reduce fairing dynamic environment generation due to separation and potentially reduce potential damage to the payload. Regarding such tongue and groove joints, the tongue is generally formed on the inner surface of the fairing, skirt, or the payload attach fitting (“PAF”) base ring or the outer surface of a closeout plate and the groove is typically formed in a separation ring, a fairing forward ring, an aft ring frame, the aft frame or between a tension cleat and other component. Some prior art systems use what is known as a single-taper tongue and groove joint. An example of one such joint is illustrated in FIG. 1, which shows the interface between an aft ring frame and a 1575-4 PAF as used with a Delta 4 launch vehicle. The exterior of the launch vehicle (also called outboard side of launch vehicle) is shown on the left of FIG. 1 and the interior of the launch vehicle (also called inboard side of launch vehicle) is shown on the right of FIG. 1. Here, the separation ring with the groove is part of the fairing/fairing aft ring frame. As illustrated, the bottom surface of the groove and the bottom surface of the tongue are non-tapered (horizontally oriented as shown, such as in launch configuration) and the upper surface of the groove and tongue are oriented at an angle relative to the horizontal. The upper surfaces of the groove and tongue are the tapered surfaces. During fairing separation, the non-tapered side of the tongue will drag along the adjacent non-tapered side of the groove until the tongue fully clears the groove. The continuing contact between the tongue and groove prolongs and continues generation of separation dynamic environments. As also shown in FIG. 1, some prior art clamping joints use tension bolts to reduce the gap between one component (e.g., the tongue on the PAF base ring) and the other component (e.g., the groove in the aft ring frame). Tension bolts are typically vertically oriented as shown, when the spacecraft is in launch configuration, and are used to reduce the gap distance between the tongue and the groove. Tension bolts are a primary source of the payload fairing (“PLF”) separation shock. Tension bolts also tend to gouge the PAF ring upon separation, which creates additional vibrations.
Other systems have implemented a minimal dual-taper tongue and groove joint, but the benefit of a minimal dual-taper is also relatively small. An example is illustrated in FIG. 2, where the joint is shown in the assembled position and the jettisoned (separated) position. The exterior of the launch vehicle is shown on the left of FIG. 2 and the interior of the launch vehicle is shown on the right of FIG. 2. The joint comprises a dual-tapered tongue 2 and a dual-taper groove 4, but the taper of the upper surfaces of the tongue 2 and groove 4 are nearly horizontal (at about a 5 degree angle) and the tapers of the lower surfaces are relatively horizontal (again, horizontal relative to the launch configuration). The groove 4 is formed on the interior surface of a skirt or fairing (also called a payload fairing or PLF) 8 and is also formed by an adjustable tension cleat 10. The fairing 8 has an inner skin panel 12 that interfaces closely to the miniskirt 6 to minimize the radial gap between the fairing 8 and PAF ring. However, there is no shimming or radial adjustment between the faces of these parts; rather, adjacent parts are sized to maintain a close fit. The tongue 2 is formed on the PAF ring, which also includes a miniskirt (also called a vertical leg) 6. The PAF ring is part of the launch vehicle upper stage. The miniskirt 6 is where the fairing 8 attaches. Here, the PAF ring is stationary and the fairing separation ring is jettisoned radially away from the PAF ring. The angled or tapered surfaces of both the tongue 2 and groove 4 will experience a growing or increasing separation distance as the groove 4 separates laterally or radially from the tongue 2 (based upon the orientation shown in FIG. 2). However, the benefit in terms of reducing shock or vibration is de minimus given the modest angle of the taper. At best, the minimal taper of the upper surfaces of the tongue 2 and the groove 4 minimally reduces the likelihood of contact during separation and generation of shock, vibration events, and/or dynamic environments.
Alternative interconnection and separation systems may use a Marman clamp band (also called a V-band clamp), which has a tongue and groove joint with tapered interfaces that “grow toward” one another such that no clearances exist between the tongue and groove when installed. Additionally, the flexible band and tensioning bolts used with the Marman clamp band require significant hoop preload, which increases shock during separation. Marman clamps are described in Marman Clamp System Design Guidelines, NASA Preferred Reliability Practices Guideline No. GDED-2214 (hereinafter, “NASA Guidelines”), which is incorporated by reference herein in its entirety. As noted in the NASA Guidelines, structural failure of Marman clamps are known to have occurred and extreme care is urged in designing such equipment.
Other disadvantages of the prior art structures, including the above systems, relate to accessibility and adjustability. The tensioning mechanisms of FIGS. 1 and 2 are located at the aft end of the aft ring and are generally accessible at that location. However, access is specifically an issue when fairings utilize a tongue and groove interface at the forward end of the fairings because the forward fairing separation ring is not accessible without internal fairing access. Also special tools are often required with these prior art systems, which compound access problems and increase expense, in addition to increased labor costs. For example, referring again to FIG. 1, there are generally between 100 and 150 tension bolts used in such separation designs. It can also be difficult and time consuming to shim, tighten, or torque a large number of tension bolts considering such activities require access between the tension bolts and the PAF base ring and forward skirt.